International Space Hall of Fame :: New Mexico Museum of Space History :: Inductee Profile USA Inducted in 1984 Established the first optical tracking system for satellites, proposed the 'dirty snowball' theory of comet formation. Fred Lawrence Whipple was born on November 5, 1906, on a farm outside of Red Oak, Iowa. While he was a teenager his father sold the farm and moved the family to Long Beach, California, where Fred worked in the family grocery store. He graduated from Long Beach High School in 1923, and enrolled in Occidental College in Los Angeles, hoping to become a professional tennis player. After transferring to the University of California at Los Angeles (UCLA), he reluctantly abandoned tennis and by his junior year became interested in astronomy. He received a Bachelor's degree in Mathematics from UCLA in 1927, then enrolled at University of California, Berkeley in 1929, teaching astronomy while pursuing a Ph.D. in the subject. After earning his doctorate in 1931, Whipple transferred to the staff of the Harvard College Observatory.

While still a graduate student, Whipple helped map the orbit of Pluto, discovered by Clyde Tombaugh in 1930. Working out of the Harvard Observatory, Whipple discovered or co-discovered five comets and asteroid 1252 Celestia. During World War II, he aided the war effort by inventing a system to counteract German radar by cutting up thousands of fragments of aluminum foil (chaff) to create false radar readings, hiding real targets with radar "static." Anticipating threats to the spacecraft of the future from space debris, in 1946, Fred Whipple invented the "meteor bumper," now known as the Whipple Shield. A thin outer skin of metal, it protects spacecraft by disintegrating space debris such as small asteroids when they impacted the shield. His invention is still used by NASA to protect spacecraft. Dr. Fred Whipple may be best known for his "dirty snowball" theory on the substance of comets in 1950. He argued that comets were primarily ice with some rock mixed in, rather than materials such as sand held together by gravity, as was the more accepted belief at the time. Dr.

Whipple believed that as a comet approached a star, light from the star vaporized ice in the comet's nucleus. The jets of particles that resulted acted like rocket engines that either slowed or accelerated the comet. He also theorized that the glowing comet tails contained particles that originated from frozen reservoirs in comet nuclei. Whipple was proven correct in 1986, when the European Space Agency's Giotto spacecraft took close-up photographs of Haley's comet. Fred Whipple was director of the Smithsonian Astrophysical Observatory (SAO) in Cambridge, Massachusetts from 1955 to 1973. Under his leadership, the SAO developed a network of Baker-Nunn cameras that achieved spectacular success in tracking man-made satellites. Anticipating the era of artificial satellites, he had organized the "Moonwatch" group to track them. His was the only organization able to make observations on Sputnik I, man's first satellite, launched by the Soviet Union on October 4, 1957. During the International Geophysical Year (1957-1958), Dr. Whipple headed a team formed by the National Academy of Sciences and the National Science Foundation, responsible for developing an optical satellite tracking system.

His techniques for photographically measuring the speeds and decelerations of meteors, his methods for computing the orbits of comets and asteroids, and his theoretical model for describing the structure of the comets are still scientific standards. President John F. Kennedy honored Fred Whipple for his tracking project with an Award for Distinguished Public Service in 1963. Whipple also received the Gold Medal of the Royal Astronomical Society in 1983, the Bruce Medal of the Astronomical Society of the Pacific in 1986, and the Henry Norris Russell Lectureship of the American Astronomical Society the next year. In 1968, Dr. Whipple set up the Mount Hopkins Observatory near Amado, Arizona. One of the world's premier observatories, it was renamed in his honor in 1982. Fred Whipple retired from Harvard in 1977, but continued to conduct astronomical research well into his nineties. Dr. Fred Whipple died in August 30, 2004, in Cambridge, Massachusetts at the age of 97.

His legacy includes asteroid 1940 Whipple, the Whipple Observatory, and the "Whipple Shield." © 2005- 2017 The New Mexico Museum of Space History , a Division of the New Mexico Department of Cultural Affairs . Photographs not the property of the New Mexico Museum of Space History appear courtesy of NASA image archives. New Mexico Museum of Space History | PO Box 5430 | Alamogordo, NM 88311-5430 575-437-2840/877-333-6589 Obituary: Fred Whipple | Science | The Guardian Fred Whipple Thursday 2 September 2004 06.40 EDT First published on Thursday 2 September 2004 06.40 EDT Close This article is 12 years old The eminent American astronomer Professor Fred Whipple, who has died aged 97, was a world-renowned expert on meteors, meteorites, comets and planetary structure. During the second world war, he worked on radar countermeasures, and later served as a senior adviser to the US space programme.

Over many years at Harvard, where he was professor of astronomy from 1950 to 1977, Whipple developed his initially controversial but now axiomatic theory that comets possess a nucleus, generally no more than a few kilometres in diameter, consisting of an aggregate of frozen gases such as the ices of methane, carbon dioxide, ammonia and water, and bonding a variety of rocky debris, including a large amount of dust and silica particles. This so-called Whipple "dirty snowball" hypothesis attracted savage criticism when it was published in the 1950s. At that time, the belief was that comets were nebulous orbiting clouds of dust and small rock particles - something like orbiting, if dispersed, sandbanks - whose changes of shape were largely determined by gravitational forces. Criticism was finally silenced in 1986 when the European Space Agency Giotto spacecraft penetrated comet Halley and photographed its cracked, rocky and outgassing nucleus, shown to be rich in frozen gases and in the form of an elliptical accreted mass estimated to be some 15km long and 7km wide.

This was a complete vindication for Whipple, who had responded to his critics with characteristic rigour, patience and only an occasional mordant comment to silence his most aggressive detractors. One of the oddities of astronomy, and probably an indication of the difficulties involved in the study of comets is that, although their mysterious visitations and superstitious interpretations are dotted throughout the pages of recorded history, there have been very few theories of their origins or structure. Throughout most of the past century, comets were regarded as an area of investigation and discovery best left to diligent amateurs. For example, in the great popular classics, which stimulated widespread interest in astronomy after the first world war such as those by Sir James Jeans, comets are barely mentioned and no attempt is made to explain how or where they are formed, or what starts their extraordinary journeys through the solar system. T his exclusion ended in 1941 when Whipple, by then already an acknowledged expert on meteors and meteorites, published a new kind of popular treatise, Earth, Moon And Planets, focusing on solar system astronomy.

This book rehearses the history of planetary astronomy and the many remaining mysteries, explains the basic techniques, and reviews recent discoveries in a form in which mathematics are minimised. In 1949 Whipple published his proposal that comets are made of the same materials as the outer planets, aggregates of ice and rock. This was buttressed in 1951 by the Dutch astronomer Jan Hendrik Oort, who pointed out that a substantial amount of material left over from the formation of the planets is now dispersed in a huge belt of asteroids which, although in solar orbit, is about a light year from the sun. Gravitational perturbations would result in a few of these small masses being shunted either out of solar orbit altogether, to become wanderers in space, or into the solar system, where they could either be captured to become periodic comets or perhaps to be seen only once as they pass through on an extra-solar trajectory.

Whipple developed these ideas, eventually explaining slight variations of cometary orbits through the propulsive forces of outgassing jets at the surface of the nucleus (actually seen by spacecraft Giotto), confirming the "tail" as a product of the solar wind and attributing the short survival of near-sun comets to their icy structure. He also promoted the development of meteor tracking systems, and investigated and helped to develop the role of radio astronomy in planetary studies. Supported by observations from around the world, including Jodrell Bank, Whipple showed that the majority of meteors visible from earth originate within the solar system and are produced predominantly from the break-up of comets. He carried out this work as director of the Smithsonian Institute Astrophysical Observatory from 1955 to 1973, and then as senior scientist there until his death. His appointment coincided with the start of the space age, and he anticipated the advent of artificial earth satellites by developing a tracking system. When the Soviet Union launched Sputnik I in October 1957, Whipple's network of amateur astronomers was the only group already set up to follow its progress, and he later co-ordinated an optical system using Baker-Nunn cameras.

This worked so well that astronomers could calculate the exact shape of the Earth from the effect of gravity on satellite orbits. B orn of country stock in Red Oak, Iowa, Whipple spent the first 15 years of his life on a farm but, because of his special abilities, was taken by his parents to California, where got a degree in mathematics at the University of California at Los Angeles. He carried out graduate and postgraduate work at Berkeley and the Lick Observatory, receiving his doctorate in 1931. He became a member of staff at the Harvard College Observatory, where he found the freedom to pursue his studies of meteors. Eventually, he became chairman of the department of astronomy (1949-56), and ultimately Phillips professor of astronomy (1968-77). After retirement, he continued as professor emeritus, cycling to the observatory six days a week until he was 90. At the office of scientific research and development within the Harvard radio research laboratories from 1942 to 1945, he directed the American programme for the development, production and operational use of "confusion reflectors", the strips of reflecting aluminium dropped from aircraft to disable enemy radar.

In 1946, back at Harvard Observatory, he began his crucial studies of comets and embarked on a lifelong involvement in civil space science as an adviser to the US government and to Nasa. In spite of his scientific rigour, Whipple's huge enthusiasm for space flight and for science fiction did not always endear him to more conventional astronomers, yet, toward the end of his life, he was able to declare himself delighted to have lived through a period during which science fiction had, in many respects, become reality. One disappointment was the inability of Nasa, because of reduced funding, to carry out the programme of cometary investigation that he was heavily involved in planning. He won a vast array of international awards, including the gold medal of the Royal Astronomical Society and, in 1963, the Distinguished Federal Civilian Service award from President Kennedy. In 1928 he married Dorothy Woods, with whom he had a son, who survives him. They divorced in 1935, and in 1946 he married Babette Samelson. She, too, survives him, as do their two daughters.

· Fred Lawrence Whipple, astronomer, born November 5 1906; died August 30 2004 This obituary has been revised and updated since the writer's own death in 1998. Fred Lawrence Whipple | HowStuffWorks Fred Lawrence Whipple NEXT PAGENEXT Whipple, Fred Lawrence (1906-) was an American astronomer who was the first to suggest that the nucleus of a comet resembled a “dirty snowball.” His research led to insights regarding the behavior of meteors and the nature of the upper atmosphere and helped establish the modern view of comets. Although Whipple made contributions in a number of areas, he was best known for his work with comets. He earned the nickname “Mr. Comet” and was considered the leading authority on the subject. In 1950, he published a landmark paper in the Astrophysical Journal on the composition of comet nuclei. Prior to this time, astronomers believed that comets resembled “floating sand banks” made up of loose particles, with no distinct body. Whipple argued that comets were more like icy conglomerates, or dirty snowballs, composed of ice water, ammonia, methane, and dust.

Up Next Clark, Alvan In 1986, Whipple's prediction was put to the test when Halley's Comet crossed Earth's orbit. Spacecraft equipped with imaging equipment and cameras were launched to get a close-up look at the comet's nucleus. Based on the measurements and photographs obtained from the space probes, researchers confirmed Whipple's “dirty snowball” model for comet nuclei. In addition to his comet research, Whipple investigated meteors, planetary nebulae, and the evolution of the solar system. Although he officially retired in 1977, he continued with his research five days a week at his Cambridge, Massachusetts, office. At age 92, he became the oldest researcher to ever take part in a NASA mission when he joined the science team working on NASA's Comet Nucleus Tour (Contour). The unmanned Contour spacecraft was supposed to fly past comets Encke and Schwassmann-Wachmann 3 and bring back images of the comets as well as an analysis of the dusts and gases in the nuclei. However, contact with the spacecraft was lost six weeks after its launch. Whipple's accomplishments include a number of inventions.

During World War II (1939–1945), he invented a chaff-cutter, which was used to create tiny pieces of aluminum foil that could be dropped from planes to confuse the enemy's radar. In the 1940's, he devised a bumper, now known as the Whipple shield, to protect spacecraft from meteors. The device is used on nearly all spacecraft. Whipple was the son of Henry Lawrence and Celestia (MacFarland) Whipple. When Whipple was 15, his family moved from their Iowa farm to California, where he completed high school. He then attended Occidental College. After completing a year at Occidental, he transferred to the University of California at Los Angeles (UCLA) and studied mathematics. In his junior year, he switched his major to astronomy. He graduated in 1927 and then attended the University of California at Berkeley. After earning his Ph.D. degree in astronomy in 1931, he left California and moved to Cambridge, Massachusetts, where he accepted a staff position at the Harvard College Observatory. Whipple's first job at Harvard was checking the accuracy of photographic plates of the sky.

To make the task more interesting, he inspected the photographic negatives for comets. In the course of this work, he discovered six comets, all of which now bear his name. Early in his career, Whipple set out to learn more about meteors. To accomplish this, he devised a two-station photographic method to measure the trajectory of meteors. Using cameras with rotating shutters, Whipple took photographs of meteors at different locations. He then studied the photographic plates to determine the meteors' atmospheric drag, velocity, and orbit around the sun. Whipple continued this research until it was interrupted by World War II (1939–1945). From his research he theorized that comets were related to meteors and had a similar composition. This line of reasoning helped him formulate the idea that comet nuclei were like dirty snowballs. In 1932, Whipple was appointed instructor in astronomy at Harvard University, advancing to lecturer six years later. During World War II, he worked on war-related research at the Harvard Radio Research Laboratories, earning a Presidential Certificate of Merit in 1948.

At the war's end in 1945, Whipple returned to Harvard where he was named associate professor. Five years later he was promoted to professor, a position he held until 1977 when he retired as Phillips Professor of Astronomy Emeritus. During his Harvard tenure, he also served as chairman of the department of astronomy. After his meteor research, Whipple studied the orbit of 40 comets to solve a problem that puzzled scientists. Astronomers were uncertain why some comets increase their orbits while others lose energy and decrease their orbits. Whipple suggested that the composition of the nucleus offered an explanation. When the comet is away from the sun and in the coldness of space, it resembles a frozen ice ball. But as a comet nears the sun, the ice begins to melt. When the ice layer evaporates. it causes gases and particles in the ice to fly away from the sun. This “jet” of gas forms the comet's coma (cloudy atmosphere) and tails. Over time, this process results in the comet losing material. Comets with large nuclei are able to withstand repeated passages around the sun, but small-nucleus comets disintegrate more quickly than would be ordinarily predicted.

This explains why certain comets fail to appear when expected. Whipple contributed to the space age in the 1950's when he developed a worldwide network of professional and amateur observers to track satellites. In 1957, when the Soviets launched Sputnik, the first satellite, Whipple's volunteers observed it and reported on the satellite's orbit. From 1955 to 1973, Whipple was director of the Smithsonian Astrophysical Observatory (SAO), a bureau of the Smithsonian Institute. At the time he took the position, the organization was based in Washington, D.C. One of his first duties was to help move the headquarters to Cambridge, Massachusetts. In 1973, the SAO merged with the Harvard College Observatory to become the Harvard-Smithsonian Center for Astrophysics (CfA). That same year, Whipple became senior scientist at the organization. In the 1960's, he codeveloped the Multiple Mirror Telescope on Mount Hopkins, near Amado, Arizona. The instrument was made up of six large telescope mirrors functioning as one, and was the first of its kind. In 1982, the Arizona facility was renamed the Fred Lawrence Whipple Observatory.

The observatory, which is part of the CfA, contains one of the largest mirror telescopes in the United States. Whipple was awarded a number of honors throughout his long and distinguished career. He received six Donahue Medals in recognition of the six comets he discovered. Other awards include the J. Lawrence Smith Medal of the National Academy of Sciences in 1949, the Kepler Medal of the American Association for the Advancement of Science in 1971, and the Distinguished Federal Civilian Service Award from President John F. Kennedy in 1963. He died in Cambridge, Massachusetts on August 30, 2004. Fred Whipple – Astronomer You are here: Home / Famous Freds / Scientific Freds / Fred Whipple - Astronomer Fred Whipple – Astronomer Fred Lawrence Whipple was an American astronomer, who worked at the Harvard College Observatory for over 70 years. Amongst his achievements, he discovered some asteroids and comets, came up with the “dirty snowball” cometary hypothesis, and designed the Whipple shield.

Born: November 5, 1906 Fred Lawrence Whipple, US astronomer - Stock Image H423/0327 - Science Photo Library Fred Lawrence Whipple, US astronomer H423/0327 Rights Managed Credit: EMILIO SEGRE VISUAL ARCHIVES/AMERICAN INSTITUTE OF PHYSICS/SCIENCE PHOTO LIBRARY Restrictions: Editorial use only Caption: Fred Lawrence Whipple (1906-2004), US astronomer. Born in Red Oak, Iowa, an early bout of polio ended his ambition to become a professional tennis player. Majoring first in mathematics, Whipple went on to receive a doctorate in astronomy in 1931 from the University of California, Berkeley. He discovered or co-discovered 7 different comets and is best known for proposing the dirty snowball hypothesis of comet composition in an influential paper published in Astrophysical Journal from 1950 to 1955. In 1955 he became director of the Smithsonian Astrophysical Observatory (SAO), remaining in the post until 1973. Release details: Model release not available. Property release not required.

Fred Whipple - Living Legends | Library of Congress Library of Congress Awarded: April 2000 (Nov. 5, 1906 - Aug. 30, 2004) Fred Whipple is the noted Harvard astronomer best known for his discoveries about the constitution and behavior of comets. Himself the discoverer of six comets, he coined the phrase “dirty snowball” to describe the physical composition of comets as collections of water, ice and other cosmic debris. In 1955, Whipple became the director of the Smithsonian Astrophysical Observatory (SAO). He also crossed paths with many astronomical giants, including the late Carl Sagan, whom he once hired for the faculty of Harvard. Dirty snowball hypothesis | Article about Dirty snowball hypothesis by The Free Dictionary Dirty snowball hypothesis | Article about Dirty snowball hypothesis by The Free Dictionary Related to Dirty snowball hypothesis: cometary comet [Gr.,=longhaired], a small celestial body consisting mostly of dust and gases that moves in an elongated elliptical or nearly parabolic orbit around the sun or another star. Comets visible from the earth can be seen for periods ranging from a few days to several months.

They were long regarded with awe and even terror and were often taken as omens of unfavorable events. In 1987 a comet orbiting the star Beta Pictoris was identified, and since then an increasing number of exocomets have been found. The Orbits of Comets Although the occurrence of many comets had been recorded, it was not until 1577 that the Danish astronomer Tycho Brahe Brahe, Tycho , 1546–1601, Danish astronomer. The most prominent astronomer of the late 16th cent., he paved the way for future discoveries by improving instruments and by his precision in fixing the positions of planets and stars. ..... Click the link for more information. suggested that they traveled in elongated rather than circular orbits. A century later Giovanni Borelli Borelli, Giovanni Alfonso , 1608–79, Italian physiologist, physicist, astronomer, and mathematician; son of a Spanish infantryman. His wide interests led to original contributions in many fields, including anatomy, epidemiology, the study of fermentation, volcanology, ..... Click the link for more information.

concluded that the orbits were parabolic and that comets passed through the solar system but once, never to return. In 1705, however, Edmond Halley Halley, Edmond , 1656–1742, English astronomer and mathematician. He is particularly noted as the first astronomer to predict the return of a comet and the first to point out the use of a transit of Venus in determining the parallax of the sun. In 1676 he went to St. ..... Click the link for more information. concluded that the comet observed in 1682 was the same one that had been described in 1531 and 1607, and he predicted that it would return again in late 1758 or early 1759.

The comet was sighted on Christmas Day in 1758, and it returned again in 1835, 1910, and 1986 (see Halley's comet Halley's comet or Comet Halley , periodic comet named for Edmond Halley, who observed it in 1682 and identified it as the one observed in 1531 and 1607. Halley did not live to see its return in 1758, close to the time he predicted. ..... Click the link for more information. ). While some comets appear to have parabolic orbits (see parabola parabola , plane curve consisting of all points equidistant from a given fixed point (focus) and a given fixed line (directrix). It is the conic section cut by a plane parallel to one of the elements of the cone. ..... Click the link for more information. ), others return to the inner solar system in highly elongated orbits with periods ranging from a hundred to thousands of years.

Still others return at shorter intervals of less than 10 years and reach aphelion (the orbital point farthest from the sun) near the planet Jupiter; these have been captured into their smaller orbits by Jupiter's gravitational attraction. Structure of Comets A comet far from the sun consists of a dense solid body or conglomerate of bodies a few miles in diameter called the nucleus. As it approaches the sun the nucleus becomes enveloped by a luminous "cloud" of dust and gases called the coma; this luminosity is caused by the molecules absorbing and reflecting the radiation of the sun. According to the icy-conglomerate theory proposed by F. L. Whipple Whipple, Fred Lawrence, 1906–2004, American astronomer, b. Red Oak, Iowa. After graduating from the Univ. of California, Berkeley (Ph.D. 1931), he accepted a position at Harvard, where he remained for the rest of his career. ..... Click the link for more information.

in 1949, the nucleus consists of frozen water and gases with particles of heavier substances interspersed throughout, thus being in effect a large, dirty snowball, although more recent research has suggested that comets may contain a higher proportion of dust and rock than previously proposed. The Stardust probe—passed near Comet Wild 2 in 2004, collected particles from the coma, and returned the samples to earth in 2006—found evidence that many of the dust particles were formed at high temperatures not found in the Oort cloud and Kuiper belt (see below), where comets are believed to have formed. Data from the Deep Impact mission, which sent a projectile crashing into Comet Tempel 1 in 2005, suggests that suggests that the interior structure of comets may consists of layers of accreted material. As the comet approaches the sun, the solar wind solar wind, stream of ionized hydrogen—protons and electrons—with an 8% component of helium ions and trace amounts of heavier ions that radiates outward from the sun at high speeds. ..... Click the link for more information.

drives particles and gases from the near the surface of the nucleus and coma to form a tail which can extend as much as 100 million mi (160 million km) in length. Thus the tail always streams out in the direction opposite the sun; i.e., it follows the head as the comet approaches the sun and precedes it as the comet passes perihelion (its closest point to the sun) and moves away. Near the sun a comet can change drastically in size and shape; it may even split into two or more pieces, as Comet Biela did in 1846, and Comet West did in 1976. The comas of comets vary widely in size, some being the size of the earth or larger. However, the nucleus, which makes up virtually all a comet's mass, is small; in 1986 the Giotto and Vega spacecrafts observed Comet Halley's nucleus to be only about 6 mi (10 km) in diameter. In 2014 Rosetta became the first space probe to orbit a comet's nucleus (that of Comet 67P); it also deployed a lander on the comet.

Comets lose material and thus brightness with successive passages near the sun. Some of this material moves around the comet's orbit as a stream of meteoroids (see meteor meteor, appearance of a small particle flying through space that interacts with the earth's upper atmosphere. While still outside the atmosphere, the particle is known as a meteoroid. Countless meteoroids of varying sizes are moving about the solar system at any time. ..... Click the link for more information. ); when the earth passes through this path, a meteor shower is observed. In 1992 the periodic comet Shoemaker Levy 9 made an extremely close passage of Jupiter. The tidal stresses induced by the giant planet's gravity shattered the comet's nucleus, estimated to have been 5–9 km (3–5 mi) in diameter, into more than 20 major fragments, the largest of which was about 4 km (2.5 mi) in diameter. Two years later, the returning fragmented comet crashed into Jupiter; observations from both terrestrial observatories and artificial satellites such as the Hubble Space Telescope yielded vast amounts of information about the structure of comets and about Jupiter's atmosphere. In 1996 the Polar satellite discovered a constant rain of small comets impacting the earth.

Unlike large comets, whose cores are estimated to be as much as 25 mi (40 km) in diameter, these are only up to 40 ft (12 m) wide. It is estimated that as many as 43,000 reach the earth each day and break up at altitudes of 600–15,000 mi (950–24,000 km). Also in 1996 the ROSAT satellite (see X-ray astronomy X-ray astronomy, study of celestial objects by means of the X rays they emit, in the wavelength range from 0.01 to 10 nanometers. X-ray astronomy dates to 1949 with the discovery that the sun emits X rays. ..... Click the link for more information. ) detected X-rays emanating from the Comet Hyakutake. This was completely unexpected, and can be explained by no known mechanism. Observation of more large comets passing through the solar system by orbiting X-ray observatories will be necessary to corroborate this finding. The Origin of Comets in the Solar System The Oort Cloud The origin of the solar system's comets is still uncertain.

They were once thought to have originated outside the solar system, but more recent theories suggest they were formed during the formation of the solar system and are permanent members of it. According to the storage-cloud hypothesis proposed by J. H. Oort Oort, Jan Hendrik , 1900–1992, Dutch astronomer. He confirmed (1927) Bertil Lindblad's theory of the Milky Way galaxy's rotation. In the 1950s he and his colleagues used radio astronomical means to map the spiral-arm structure of the galaxy. ..... Click the link for more information. and since modified, a spherical shell of more than 100 billion comets surrounds the solar system at a distance of 20,000 AU to 50,000 AU or greater (1 AU, or astronomical unit, being the mean distance from the earth to the sun); some astronomers have suggested an inner Oort cloud exists beginning at 2,000 to 5,000 AU and extending to 20,000 AU.

While the comets move very slowly in this huge storage cloud, a passing star may change the orbits of bodies in the outer reaches of the Oort cloud enough to force some of them into the inner part of the solar system. The mechanism for the Oort cloud's creation, however, is unclear; it has been suggested that the Oort cloud may include a significant amount of material that originated outside the solar system and was gravitationally captured by the sun. The Kuiper Belt In 1951, G. P. Kuiper Kuiper, Gerard Peter or Gerrit Pieter , 1905–73, American astronomer, b. the Netherlands. Kuiper is considered to be the father of modern planetary science for his wide ranging studies of the solar system. ..... Click the link for more information. , noting that Oort's cloud of comets did not adequately account for the population of short-period comets (those making complete orbits around the sun in less than 200 years), proposed the existence of a disk-shaped region of minor planets outside the orbit of Neptune, now called the Kuiper belt, as a source for such comets.

The Kuiper belt acts as a reservoir for these in the same way that the Oort cloud acts as a reservoir for the long-period comets. This theory was validated in 1992 with the discovery of the first of the more than 70,000 so-called transneptunian objects, bodies more than 60 mi (100 km) in diameter in an orbit 30–50 AU from the sun. Astronomers regard Pluto Pluto, in astronomy, a dwarf planet and the first Kuiper belt, or transneptunian, object (see comet) to be discovered (1930) by astronomers. Pluto has an elliptical orbit usually lying beyond that of Neptune. ..... Click the link for more information. not as a planet but rather as dwarf planet dwarf planet, a nonluminous body of rock or gas that orbits the sun and has a rounded shape due to its gravity. Unlike a planet, a dwarf planet is not capable of clearing its orbit of smaller objects by collision, capture, or other means. ..... Click the link for more information. that is a member of the Kuiper belt. The discoveries of several Kuiper belt objects led to this view.

Eris Eris, in astronomy, the largest known dwarf planet. Eris, whose highly eccentric elliptical orbit ranges from 38 AU to 97 AU and is inclined more than 44°, is the largest known object of the Kuiper belt (see comet), with a diameter (1,445 mi/2,317 km) slightly larger than ..... Click the link for more information. , an object discovered in 2003 (and originally nicknamed Xena), has an elongated orbit that extends to roughly three times the distance of Pluto's, has a diameter (1,500 mi/2,400 km) slightly larger than that of Pluto, and has a moon; Quaoar is more than half the size of Pluto; and Ixion and Varuna are almost half the size of Pluto. 2003 VS2 (roughly a fourth the size of Pluto) and a number of other Kuiper belt objects, called plutinos, have an orbital synchrony with Neptune like that of Pluto (Neptune completes three orbits around the sun in the same time that Pluto and the plutinos complete two orbits). Bibliography See D.

Yeomans, Comets (1991), C. Sagan and A. Druyan, Comet (1997), D. H. Levy, Comets (1998), G. Kronk, Cometography (1999), and D. J. Eicher, Comets! (2013). comet A minor member of the Solar System that travels around the Sun in an orbit that generally is much more eccentric than the orbits of planets. Typical comets have three parts: the nucleus , coma , and comet tail . The gas and dust tails of a comet appear only when the comet is near the Sun and always point away from the Sun. The nucleus is the permanent solid portion of a comet and is thought by the majority of astrophysicists to be a kilometer-sized dirty snowball; this model – the Whipple model – was first suggested by Fred L. Whipple in 1951. The Solar System contains only a few observable comets that have nuclei in the tens of kilometers size range. The numbers of actual (as opposed to observed) comets increase enormously as one goes to smaller and smaller sizes, but these are much less easy to see.

The satellite missions to Halley's comet have revealed much about cometary composition and obtained the first image of a nucleus. Cometary orbits fall into two classes. Short-period comets have periods of less than 200 years and orbits lying completely or almost completely inside the planetary system. They seem to have been captured into the inner Solar System by the gravitational attraction of the major planets. At any epoch about 50 of these are bright enough to be detected as they come to perihelion . They have a mean eccentricity of 0.56 and a mean inclination of 11°. Nearly all of them (Halley's comet is an exception) are moving in direct orbits, i.e. in the same direction as the planets. The second class have near-parabolic orbits with periods in excess of 200 years. These orbits are orientated at random, indicating that these comets do not come from any specific direction in space. Many of them have been seen only once (for example Kohoutek has a period in excess of 70 000 years). The majority of comets observed from Earth have perihelions near the Earth. This is simply due to observational selection.

The brightness of a comet is proportional to 1/rn δ2, where r is the distance between the comet and the Sun and δ is the comet–Earth distance. The power n is on average 4.2 but can vary widely around this value. On average a comet passes perihelion about 1000 times before decaying away. Cometary decay produces meteoroid streams . Comets are named after their discoverers. In any year, say 1994, comets are designated 1994a, 1994b, etc., in order of discovery. Permanent designations 1994 I, 1994 II, etc., are given later, these being in order of date of perihelion passage. There are two prevalent theories of cometary origin. In the first theory comets were produced as icy planetesimals in the Saturn–Neptune region, at the same time as the origin of the Solar System, and were then stored in the Oort cloud . In the second they are produced by gravitational accretion every time the Sun passes through an interstellar dust cloud.

This latter theory predicts that the Solar System's cometary reservoir is periodically being topped up. The first theory predicts a cometary population that decreases with time. Comet a body of the solar system having the appearance of a nebulous object usually with a bright concentration—the nucleus—at the center and a tail. General information A comet is observed when a small icy body, the nucleus of the comet, approaches to within 4–5 astronomical units (AU) of the sun, is heated by the sun’s rays, and begins to give off gas and dust. The gas and dust form a nebulous envelope (the comet’s atmosphere), sometimes called the coma, around the nucleus; together with the nucleus it constitutes the comet’s head. The comet’s atmosphere continuously dissipates into space and exists only as long as gas and dust continue to emanate from the nucleus. Under the influence of radiation pressure and owing to interaction with the solar wind, the gas and dust are carried away Árom the nucleus, forming the comet’s tail. In most comets a bright “nucleus” (either starlike or diffuse) is observed in the middle of the head. This is the glow of the central, denser zone of gases around the comet’s true nucleus.

The comet’s head and tail are not well defined; their apparent dimensions depend on the total intensity of gas and dust emissions from the nucleus and its proximity to the sun, on the one hand, and on the observational circumstances, primarily the background brightness of the sky, on the other. Ancient Chinese annals contain significant information on sightings and motion of comets. But in Europe, in accordance with Aristotle’s ideas, it was thought until the 17th century that comets originated and traveled in the atmosphere, that they were terrestrial vapors that had risen upward and been ignited on approach to the “sphere of fire,” and that, moreover, their tails were flames driven by the wind. Tycho Brahe, studying the motion of the comet of 1577 among the stars, determined its parallax from observations in Denmark and Prague. It proved to be less than the lunar parallax, and thus the comet was more distant then the moon. This was proof that comets were celestial bodies, like the moon and the planets. After the discovery of the law of gravitation, methods for determining cometary orbits were worked out in the 18th and 19th centuries (E. Halley, H. Olbers).

A new approach to comet research was proposed by F. Bessel (at the beginning of the 19th century) and developed by F. A. Bredikhin (in the second half of the 19th century), who began to study the physical nature of comets and the features of their internal structure. In particular, Bredikhin created a mechanical theory of comet shapes, which has played a large role in comet research. At the beginning of the 20th century an Austrian astronomer and the Soviet astronomer S. V. Orlov investigated the brightness of comets and established the law of the dependence of its variation on the comet’s distance from the sun. The modern era in comet research began in 1910 with the return of the bright Halley’s Comet, when photographic and spectroscopic methods of observation were widely used. The unexpected apparitions of unusual celestial bodies, such as bright comets, have always made a strong impression on man. Therefore, it is not surprising that superstitious people saw the apparitions of comets as portents and linked them with local terrestrial events.

Thus, for example, the appearance of a bright comet in 1811–12 was connected in Russia with Napoleon’s invasion, in Spain with the good grape harvest, and in Mexico with the discovery of silver ores. The number of comets in the solar system is extremely large, probably reaching hundreds of billions. However, only a small number of comets are accessible to observation, namely, those passing within the orbit of Jupiter. Thus, in the period from 1850 to 1949 an average of about five comets were annually observed passing through perihelion, of which only one was visible to the naked eye. In the subsequent 20 years (1950–69), this number increased to nine per year owing to the intensification of comet searches. Table 1 lists the brighter comets of the 19th and 20th centuries and their greatest magnitude (where known). Table 1.

Bright comets FRED WHIPPLE - A LIFETIME OF SOLVING COMETARY RIDDLES - NYTimes.com FRED WHIPPLE: A LIFETIME OF SOLVING COMETARY RIDDLES By WALTER SULLIVAN Published: January 14, 1986 THE man credited with originating the widely accepted concept of comet heads as ''dirty snowballs'' was not told about Halley's comet when it last crossed his skies in 1910. It was not table talk on his father's Iowa farm. Fred L. Whipple was then 3 years old. Seventeen years later the farm-boy-turned-astronomer, as a graduate student at the University of California in Berkeley, began a series of diverse observations that, when they all fell into place in the late 1940's, led to his snowball hypothesis. That theory is now destined to be extensively investigated as European, Japanese and Soviet spacecraft converge on Halley's comet for a succession of flybies in March. In an interview as Dr. Whipple was preparing to give a lecture on Halley's comet, he described the succession of discoveries pointing toward the snowball or ''icy conglomerate'' concept.

He also offered an explanation of why the comet may be only half as bright as it was when it was recorded by the Chinese in 240 B.C. Loss of Brightness While current difficulties in seeing Halley's are chiefly attributed to the great distance from the earth of its current passage as opposed to the last one in 1910, it also appears to have become less bright intrinsically. Dr. Whipple cited the calculations of David Hughes of Sheffield University in England based on distances at which the comet was first seen each time it returned and when it vanished as it departed. From this he has deduced, with an admittedly large margin of error, that it has gradually become dimmer - perhaps through having shed part of its material - and was twice as bright when it was seen by the Chinese more than 2,100 years ago. He explained that his earliest work on comets, published when he was 20, was a series of predictions on cometary orbits. The predictions were based, as those of Edmond Halley were three centuries earlier, on the use of logarithms as mathematical tools, since computers had not yet appeared.

He was aided, however, by a method newly developed at Berkeley by the astronomer A. O. Leuschner. In this way, Dr. Whipple was able to extrapolate the course of a comet in the future from its observed position in the past. Dr. Whipple turned to astronomy after a bout with polio made it clear that he would not be able to fulfill his dream of becoming a tennis champion. His predictions of cometary positions were published in an announcement card by the Harvard College observatory for the benefit of other observers. Doubts on Earlier Theory After World War II, Dr. Whipple came to doubt the prevailing view of comets as ''flying sand banks,'' partly as a result of his observations of meteors. At the time it was believed that comets were composed of loose material that, when shed, formed comet tails and later fell into the atmosphere as meteors or ''shooting stars.'' It was known that meteor showers typically occur on days when the earth crosses the orbits of various comets, passing through debris shed by them in the past. Like grains of sand the debris plunges into the atmosphere at such high velocity that it glows brilliantly for a second or two. Dr.

Whipple, by then at Harvard, used photographic records of meteors obtained simultaneously from the university at Cambridge and the village of Harvard to the west. The cameras chopped streaks formed by the meteors into dashes indicating their speed and their slowing by atmospheric drag. From images obtained at both sites, it was possible to calculate the meteors' orbits and the height at which they began to glow. From the rate at which they were slowed, it became possible to increase from 30 to 60 miles the height at which scientists were able to estimate atmospheric density. What in particular interested Dr. Whipple were the orbits of meteors attributed to Clement Encke, a comet that returns every three and a half years - more often than any other. Encke, it had been found, is always ''late'' in that some effect slows each orbit. Halley, too, was typically three to four days late, whereas other comets sometimes came back ''too soon'' as though accelerated in some manner. Makeup of Comets Dr. Whipple noted that fragments of the molecules of water, ammonia and methane had been detected in spectral analyses of light radiated by material shed by comets to form their tails.

This led him to conclude that the comet heads contained voluminous gases in frozen form as well as the solid material observed in meteors. Otherwise, he said, ''a comet would have run out of gas in no time.'' Furthermore, he added, a large reservoir of frozen gas could account for the speeding up or slowing down of comets like Encke. If solar heating drives gas off the sun-facing side of the comet as the comet rotates, that escaping gas will reach full force once that side has rotated away from the sun. This can act like a jet pushing the comet either forward in its orbit, causing it to arrive early, or backwards, depending on the direction of orbital flight and rotation. Such an effect could explain the diversity of paths detected in the Encke meteors, but it also implied that the changes had occurred over hundreds if not thousands of years. Forecast Is Borne Out ''I knew,'' Dr. Whipple said, ''that Encke had been there for a long, long time. And he predicted that its debris would also fall to the earth when the other side of its orbit was crossed by the earth during daylight in late June. Those meteors have subsequently been detected by radar.

He pointed out that a comet like Halley's with a nucleus about five miles in diameter sheds roughly 200 million tons of material on each trip into the inner solar system - a reduction of three to six feet in its radius. If, he proposed in 1950, comets like Encke were merely loose sand banks, they would have disintegrated long ago. It had to be a solid object - a massive conglomerate of dust and frozen gases. Since the high velocity outflow of gas from the sun or solar wind is believed to account in part for comet tails, Dr. Whipple was asked whether the failure of Halley so far to develop a prominent tail was related to the current paucity of sunspots and low level of solar activity. He noted that some theories actually predict larger comet tails during such periods. In any case, he believes a more dramatic tail may be evident after the comet rounds the sun in early February. photo of Dr. Fred Whipple DATA SHOW NUCLEUS OF HALLEY'S COMET BLACKER THAN COAL - NYTimes.com DATA SHOW NUCLEUS OF HALLEY'S COMET BLACKER THAN COAL By JAMES M.

MARKHAM; Special to The New York Times Published: March 15, 1986 DARMSTADT, West Germany, March 14— Elated scientists at the European Space Agency said today that the spinning Giotto craft that streaked past the heart of Halley's comet early this morning revealed the comet's mysterious nucleus to be extremely dark, rough and irregular, and bigger than had been thought. ''There's no question that the true color of the nucleus is black, absolutely black, blacker than coal, almost like velvet,'' Horst Keller, an agency scientist, told a crammed news conference called to give preliminary results from the Giotto probe. ''It's very dark, the darkest dark you can imagine.'' ''Since the nucleus is so dark, it must be warm,'' said Mr. Keller, who said the comet appeared to be covered with a black crust. ''The ice has to come from deeper in,'' he added. The data from Giotto, the last of five missions to Halley's comet in its journey around the Sun, go a long way toward drawing a picture of the comet, whose makeup was largely a matter of hypothesis a few weeks ago.

The notion of Halley's comet as a coal-black body challenged its earlier popular image as ''a dirty snowball.'' But Fred Whipple, the American astronomer who first used the snowball metaphor, told the news conference that he was ''truly delighted'' with Giotto's close-up photographs. ''The extreme darkness was to be expected from very fine dust embedded in ice,'' said the Harvard astronomer, who noted that dust activity and solar winds around the comet were lower than when two Soviet craft passed it at a far greater distance earlier this month. For several years infrared observations of comets made by ground-based telescopes have indicated that comets are certainly not pristine balls of ice but apparently contained a considerable amount of dark dust. Dr. Donald K. Yeomans, an astronomer at the Jet Propulsion Laboratory in Pasadena, Calif., said the Giotto findings suggested that comets may have even more black dust than had been imagined but that they are ''still substantially ice bodies.'' He said the discovery was a significant confirmation of what many scientists had theorized and did not contradict Dr. Whipple's ''dirty snowball'' hypothesis. Excited by the fresh findings about a celestial body that has fascinated man for centuries, Mr.

Keller and other scientists said that the peanut-shaped comet had emitted jets of what appeared to be melted ice and dust that might have disrupted the Giotto's antenna as the European spacecraft raced within 335 miles of the core. 'Centers of High Activity' ''There are centers of high activity where beams of dust are coming out of it,'' said Mr. Keller of the comet's nucleus. ''Almost all of the activity is toward the Sun.'' Rudiger Reinhard, the mission's project scientist, said one of the greatest surprises was the extreme ''heterogeneity'' of the dust-filled atmosphere around the comet, which gave off particles in irregular bursts and not in a uniform manner, as some had thought. European Space Agency scientists said they had dramatic photographs of these ''jets'' that were being studied before being released. At 1:10:58 A.M., two seconds before the space probe made the closest approach ever to the comet's nucleus, bombarding dust particles knocked the Giotto slightly off course, pointing its antenna away from the Earth and interrupting the transmission of data. But 34 minutes later ground stations in Australia recovered the wobbly craft's signal and the Giotto resumed data transmission.

Its camera, however, had ceased emitting images of the comet 8,104 miles from the closest approach point, according to Mr. Keller, meaning that the mission had no photographs as the Giotto emerged on the other side. New Data on Dimensions The German scientist said that the latest analysis of data showed that Halley's comet was 9.3 miles long and ''at least'' 2.5 miles wide, larger than estimated even early this morning, minutes after the encounter in space about 90 million miles from the Earth. Although the loss of contact with the craft two seconds before its closest encounter had spread confusion and despondency early this morning, the agency scientists and others from the United States, the Soviet Union and Japan this afternoon pronounced the Giotto mission a triumph. ''I can tell you the mission is accomplished beyond all expectations since we have survived the encounter and some experiments are still providing data at this time,'' said Roger Bonnet, the director of programs at the 11-nation agency. At 10 o'clock this morning the Darmstadt ground control reported that the spacecraft was performing operations and that 4 of 10 experiments on board were continuing to function.

Damage From Encounter An initial report found that there had been no damage to the Giotto's power supply or solar panels or to the mechanism that keeps the antenna on the spinning craft pointed toward the Earth. But the report said temperature increases at the craft's lower end had indicated a rupture of insulation blankets and possible damage to its dust-protection system. In the next few days, Mr. Bonnet said, a command will be given to the Giotto to bring it down to 12,420 miles from the Earth by July 1990 but that the agency did not intend to try to recover the craft. ''We are preparing Giotto for a future mission by putting it in a parking orbit,'' said Mr. Bonnet.

Question: What was the subject of astronomer Fred Whipple's 'Dirty Snowball' hypothesis?
Answer: Comets